Browsing by Author "Huang, HF"

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    Corrosion performance of Ni-16%wt.Mo-X%wt.SiC alloys in FLiNaK molten salt
    (Elsevier, 2018-10-01) Yang, C; Muránsky, O; Zhu, HL; Karatchevtseva, I; Holmes, R; Avdeev, M; Jia, YY; Huang, HF; Zhou, XT
    The corrosion performance of Ni-16%wt.Mo-X%wt.SiC (X = 0.5, 1.5, 2.0, 2.5 and 3.0) alloys prepared via mechanical alloying followed by consolidation using spark plasma sintering (SPS) from pure Ni, Mo and SiC powders is investigated. Corrosion testing at 650 °C/200 h in FLiNaK molten salt showed that increasing the volume fraction of SiC in the initial Ni-Mo-SiC powder mixture leads to formation of large amount of Mo2C precipitates, which readily dissolve into FLiNaK molten salt. Hence, only the corrosion resistance of NiMo-SiC alloys with a low SiC content (<2 wt.%) is comparable to that of Hastelloy-N® alloy. © 2018 Elsevier Ltd. All rights reserved.
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    Corrosion performance of Ni-based structural alloys for applications in molten-salt based energy systems: experiment & numerical validation
    (Elsevier, 2021-09) Lee, M; Muránsky, O; Karatchevtseva, I; Huang, HF; Laws, KJ
    The molten salt corrosion performance of a Y2O3-strengthened Ni-Cr alloy (MA754®) designed for high temperature applications (> 750 °C) was compared to purpose-designed Ni-Mo-Cr molten-salt resistant alloys (GH3535, HASTELLOY-N®). The significant material mass loss of MA754® alloy is attributed to its higher Cr-content. However, Y2O3 dispersoids are shown to play only a minor role in the corrosion performance of this oxide-dispersion-strengthened (ODS) alloy. The current result, thus, points to the possibility for the development of low Cr-content ODS alloys that combines the high-temperature properties of ODS MA754® alloy with good molten salt corrosion resistance of well-established GH3535 and HASTELLOY-N® alloys. Crown Copyright © 2021 Published by Elsevier Ltd
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    Defect evolution in a NiMoCrFe alloy subjected to high-dose Kr ion irradiation at elevated temperature
    (Elsevier B.V., 2016-06-01) de los Reyes, M; Voskoboinikov, R; Kirk, MA; Huang, HF; Lumpkin, GR; Bhattacharyya, D
    A candidate NiMoCrFe alloy (GH3535) for application as a structural material in a molten salt nuclear reactor was irradiated with 1 MeV Kr2+ ions (723 K, max dose of 100 dpa) at the IVEM-Tandem facility. The evolution of defects like dislocation loops and vacancy- and self-interstitial clusters was examined in-situ. For obtaining a deeper insight into the true nature of these defects, the irradiated sample was further analysed under a TEM post-facto. The results show that there is a range of different types of defects formed under irradiation. Interaction of radiation defects with each other and with pre-existing defects, e.g., linear dislocations, leads to the formation of complex microstructures. Molecular dynamics simulations used to obtain a greater understanding of these defect transformations showed that the interaction between linear dislocations and radiation induced dislocation loops could form faulted structures that explain the fringed contrast of these defects observed in TEM. © 2016 Elsevier B.V.
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    The effect of applied stress on the high-temperature creep behaviour and microstructure of NiMoCr Hastelloy-N® alloy
    (Elsevier, 2021-05) Zhu, HL; Muránsky, O; Wei, T; Davis, J; Budzakoska-Testone, E; Huang, HF; Drew, M
    The high-temperature creep behaviour and microstructural evolution of Hastelloy-N® was investigated using miniaturised creep samples tested under vacuum at 973 K (700 °C) and stresses of 100 MPa and 165 MPa. The higher applied stress reduced the creep life of the alloy sevenfold, and the creep mechanism at 165 MPa was predominately dislocation-creep while the creep mechanism at 100 MPa was a combination of dislocation creep, diffusion creep and grain boundary sliding. The post-creep microstructure examination using Electron Back-Scatter Diffraction (EBSD) technique showed significantly larger number of Low-Angle Grain Boundaries (LAGBs) and Geometrically-Necessary Dislocations (GNDs) formed during creep at 165 MPa than at 100 MPa. On the other hand, the microstructure of the sample tested at 100 MPa revealed more pronounced precipitation of secondary carbides along High-Angle Grain Boundaries (HAGBs) due to the longer exposure to high temperature. The precipitation of secondary carbides along grain boundaries resulted in grain boundary embrittlement and the promotion of intergranular cracking, which then resulted in low strain-to-failure in the low-stress creep test sample. In addition, it is shown that the prolonged exposure to the elevated temperature lead to Cr depletion from the matrix, reducing solid solution strengthening during creep. © 2021 Acta Materialia Inc. Published by Elsevier B.V.
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    The effect of grain size and dislocation density on the tensile properties of Ni-SiCNP composites during annealing
    (Springer Nature, 2016-02-12) Yang, C; Huang, HF; Thorogood, GJ; Jiang, L; Ye, XX; Li, ZJ; Zhou, XT
    The grain size refinement, enhancement of mechanical properties, and static recrystallization behavior of metallic nickel-silicon carbide nano-particle (Ni-3wt.%SiCNP) composites, milled for times ranging from 8 to 48 h have been examined. One set of Ni-SiCNP composite samples were annealed at 300 °C for 250 h, while the other set of samples were maintained at room temperature for control purposes (reference). The electron backscatter diffraction results indicate that the grain size of the annealed Ni-SiCNP composite was refined due to grain restructuring during static recrystallization. The x-ray diffraction results indicate that low-temperature annealing effectively reduced the density of dislocations; this can be explained by the dislocation pile-up model. Additionally, the tensile tests indicated that the annealed Ni-SiCNP composite had a significant increase in strength due to an increase of the Hall–Petch strengthening effect with a slight increase in the total elongation. The decrease of dislocation pile-up in the grain interiors and the increase in grain boundary sliding are assumed to be the main mechanisms at play. The relationship between the microstructural evolution and the variation of tensile properties is examined in this study. © 2016 ASM International. Published by Springer Nature.
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    The effect of milling time on the microstructural characteristics and strengthening mechanisms of NiMo-SiC alloys prepared via powder metallurgy
    (Multidisciplinary Digital Publishing Institute, 2017-04-06) Yang, C; Muránsky, O; Zhu, HL; Thorogood, GJ; Avdeev, M; Huang, HF; Zhou, XT
    A new generation of alloys, which rely on a combination of various strengthening mechanisms, has been developed for application in molten salt nuclear reactors. In the current study, a battery of dispersion and precipitation-strengthened (DPS) NiMo-based alloys containing varying amounts of SiC (0.5–2.5 wt %) were prepared from Ni-Mo-SiC powder mixture via a mechanical alloying (MA) route followed by spark plasma sintering (SPS) and rapid cooling. Neutron Powder Diffraction (NPD), Electron Back Scattering Diffraction (EBSD), and Transmission Electron Microscopy (TEM) were employed in the characterization of the microstructural properties of these in-house prepared NiMo-SiC DPS alloys. The study showed that uniformly-dispersed SiC particles provide dispersion strengthening, the precipitation of nano-scale Ni3Si particles provides precipitation strengthening, and the solid-solution of Mo in the Ni matrix provides solid-solution strengthening. It was further shown that the milling time has significant effects on the microstructural characteristics of these alloys. Increased milling time seems to limit the grain growth of the NiMo matrix by producing well-dispersed Mo2C particles during sintering. The amount of grain boundaries greatly increases the Hall–Petch strengthening, resulting in significantly higher strength in the case of 48-h-milled NiMo-SiC DPS alloys compared with the 8-h-milled alloys. However, it was also shown that the total elongation is considerably reduced in the 48-h-milled NiMo-SiC DPS alloy due to high porosity. The porosity is a result of cold welding of the powder mixture during the extended milling process. © This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
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    Effect of tellurium (Te4+) irradiation on microstructure and associated irradiation-induced hardening
    (IOP Publishing, 2021-04) Huang, HF; Liao, JZ; Lei, GH; Muránsky, O; Wei, T; Ionescu, M
    The GH3535 alloy samples were irradiated using 15-MeV Te4+ ions at 650 °C to a dose of 0.5, 3.0, 10, and 20 dpa, respectively. The Te atoms distribution and microstructure evolution were examined by electron probe microanalysis (EPMA) and transmission electron microscopy (TEM). The nano-indenter was then used to measure the nano-hardness changes of samples before and after irradiation. TEM results showed the formation of dislocation loops in the irradiated samples. Their mean diameters increase with the increase of irradiation dose and tends to be saturated when irradiation dose exceeds 10 dpa. The ratio of yield strength increments calculated by dispersed barrier hardening (DBH) model is basically consistent with that of nano-hardness increments measured by nano-indenter. In addition, the relationship between the nano-hardness increments and dpa for the GH3535 alloy irradiated by Te ions has been revealed in the study. © 2021 Chinese Physical Society and IOP Publishing Ltd
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    Helium ion irradiation behavior of Ni-1wt.%SiCNP composite and the effect of ion flux
    (Elsevier, 2015-12) Zhou, XL; Huang, HF; Xie, R; Thorogood, GJ; Yang, C; Li, ZJ; Xu, HJ
    Silicon carbide nanoparticle-reinforced nickel metal (Ni–SiCNP composite) samples were bombarded by helium ions with fluences of 1 × 1016 and 3 × 1016 ions/cm2 at two different fluxes. The microstructural and mechanical changes were characterized via TEM and nanoindentation. Nano-scaled helium bubbles in the shape of spheres were observed in the samples irradiated at high flux and polygons at low flux. The number of helium bubbles increased with the fluence, whereas their mean size remained unaffected. In addition, the nanohardness of the damage layer also increased as the fluence increased. In addition this study suggests that a higher flux results in a higher number of smaller helium bubbles, while showing no obvious effect on the irradiation-induced hardening of the materials. © 2015 Elsevier B.V
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    On development of NiMo-SiC alloys via powder metallurgy for the use in molten salt environment
    (Engineers Australia, 2017-11-27) Yang, C; Muránsky, O; Zhu, HL; Avdeev, M; Huang, HF; Huai, P; Zhou, XT
    A new generation of alloys, which rely on a combination of various strengthening mechanisms, has been developed for application in molten salt environment, namely in future molten salt reactors (MSR), and concentrating solar power (CSP) plants. In the current study, a battery of NiMo-based alloys containing varying amounts of SiC (0.5-2.5 wt%) were prepared by mechanical alloying from Ni-Mo-SiC powder mixture, The mechanical alloying was followed by spark plasma sintering and rapid cooling. Neutron Powder Diffraction (NPD), Electron Back Scattering Diffraction (EBSD) and Transmission Electron Microscopy (TEM) were employed in the characterization of the microstructural properties of these in-house prepared NiMo-SiC alloys. The present study shows that uniformly-dispersed SiC particles provide dispersion strengthening, the precipitation of nano-scale Ni3Si nano-precipitates provides precipitation strengthening, and the solid-solution of Mo in the Ni matrix provides solid-solution strengthening. In addition, formed Mo2C particles limit the grain growth of NiMo matrix thus further increasing the strength of these NiMo-SiC via Hall-Petch strengthening. As a result, these newly developed NiMo-SiC alloys possess superior strength in comparison to conventional forged NiMo alloys. However, it is shown that the cold welding of powders during the mechanical alloying leads to porosity, which might then lead to reduced ductility.© 2017 Engineers Australia
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    On the irradiation tolerance of nano-grained Ni–Mo–Cr alloy: 1 MeV He+ irradiation experiment
    (Elsevier, 2021-02) Zhu, ZB; Huang, HF; Muránsky, O; Liu, JZ; Zhu, ZY; Huang, Y
    The irradiation damage behavior was studied in the nano-grained Ni–Mo–Cr alloy (nano-grained GH3535), which was irradiated by He ion to various dose. The evolution of defects and hardness changes are characterized by transmission electron microscopy and nanoindentation to explore the irradiation tolerance of the nano-grained GH3535 and the coarse-grained GH3535 (annealed GH3535), where the later was chosen as reference material to make comparison with nano-grained GH3535. The results show that though both the average size and number density of He bubbles increase with an increase in the irradiation dose, the smaller volume fraction is found in the nano-grained GH3535 compared with the coarse-grained GH3535 under the same irradiation condition. This indicates that the nano-grained GH3535 possess better irradiation swelling resistance than the coarse-grained GH3535. However, the increase in the hardness of the nano-grained GH3535 is more significant than in the coarse-grained GH3535 under the same irradiation dose. This suggests stronger irradiation-induced hardening of the nano-grained alloy comparing to coarse-grained alloy, due to the impeding effect caused by grain boundaries decorated with He bubbles. This study provides insight into the design of irradiation-tolerant nickel-based alloys for nuclear industry applications. © 2020 Elsevier B.V
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    On the origin of strengthening mechanisms in Ni-Mo alloys prepared via powder metallurgy
    (Elsevier, 2017-01-05) Yang, C; Muránsky, O; Zhu, HL; Thorogood, GJ; Huang, HF; Zhou, XT
    A new class of materials, which rely on the dispersion strengthening of SiC particles in addition to precipitation strengthening by nano-precipitates is being developed for the application in molten salt nuclear reactors. A battery of dispersion and precipitation strengthened (DPS) NiMo-based alloys containing varying amount of SiC (0.5–2.5 wt.%) was prepared via a mechanical alloying (MA) route followed by spark plasma sintering (SPS), rapid cooling, high-temperature annealing and water quenching. Lab X-ray Diffraction (XRD), Electron Back Scattering Diffraction (EBSD), and Transmission Electron Microscopy (TEM) were employed in the microstructural characterization of this new type of alloys. It is shown that the NiMo matrix of these alloys is effectively reinforced by dispersion of SiC from the initial powder mixture and nano-Ni3Si precipitates, which precipitated during the sintering/annealing process. Furthermore, the matrix is strengthened by solid-solution of Mo in Ni. As a result, these newly developed NiMo alloys take advantage of dispersion, precipitation and solid solution strengthening, which leads to their superior mechanical properties. © 2016 Elsevier Ltd